The present invention relates generally to the installation and retention of a low friction pad at the ends of the supporting leaves of a vehicular leaf spring to improve ride characteristics and reduce noise and wear between adjacent leaves of a multi-leaf spring assembly during operation of a vehicle.
For many years, non-metallic, generally polymeric, tip inserts or separator pads have been used between adjacent vehicular leaf spring plates (or leaves), as a means of reducing friction, noise and wear and improving ride as the plates slide relative to each other when the spring flexes during operation of vehicle. Examples involving the use of leaf spring separator pads at the ends of the leaves which support the main leaf attached to the vehicle chassis may be found In U.S. Pat. Nos. 5,219,151 and 5,706,559. The most common and expedient approach to attachment is to integrally mold a projecting solid or tubular shank or post on the underside of the tip insert pad which is then inserted in a through hole centrally located near the ends or tips of some or all of the supporting leaves and second stage leaves in a multi-leaf spring assembly.
Prior leaf spring tip inserts have been commonly designed following either or both of two approaches. The first has been specification of an intentional interference fit between the diameter of the tip insert post or shank and the diameter of the receiving hole in the spring leaf relying on compression of that polymer shank and resulting radial forces and friction with the surface of the receiving hole in the spring leaf to accomplish tip insert retention. The second and most common means has been to provide some form of an integrally molded radial projection or protuberance near the free end of the tip insert shank which substantially exceeds the diameter of the receiving hole in the spring leaf. Such a tip insert design commonly employs a tubular shank with two or more axial slots through the shank wall to allow inward deflection of the post to accommodate passing of the said shank end projection through the receiving hole in the spring leaf. When the shank is fully inserted in the leaf spring plate the projection extends beyond the lower surface of the spring and overlaps the outer edges of the receiving hole to achieve retention of the tip insert in vehicle service.
It is recognized that it is desirable to provide a tip insert that may be easily installed with minimum force using simple tools, but requires high force to be removed or disengaged once it has been installed in the spring leaf. Generally tip inserts which are the easiest to install provided the least retention to the leaf spring as a result of the lack of sufficient interference fit of the tip insert shank diameter with the receiving hole and/or the amount of overlap of the shank end protuberance with the receiving hole. Increasing the interference fit and/or the overlap of the tip insert shank end protuberance with its receiving hole in the spring leaf has been employed to increase the reliability of tip insert retention, as measured by the force to push the tip insert shank in reverse, back out of the hole in the spring leaf. However, the degree of difficulty and force required to insert the shank through the hole in the spring plate increases greatly in this situation and results in a high level of permanent deformation of the polymer shank and/or the radial protuberance which decreases its ultimate interference and retention capability. As a result, the retention capability and reliability of past tip insert designs has been limited and less than needed to achieve acceptable durability in many vehicle leaf spring applications.
To fulfill the above-noted and other unmet desires, the revelation of the present invention is brought forth. The present invention provides a leaf spring tip insert which requires high force to be removed from the spring leaf, but can be manually installed relatively easily with simple hand tools. In a preferred embodiment, the present invention provides a leaf spring tip insert that includes a pad portion providing a low friction, wear-resistant separator between adjacent leaf spring tips. Extending from the pad portion is at least one shank portion that has a central bore and a plurality of axial slots starting from a free end of the shank. The shank also has protuberances extending radially outward therefrom with leaf spring engagement surfaces facing toward the pad portion at an axial distance therefrom. The protuberances are dimensionally adapted and configured so that the shank and protuberances are deflected and compressed radially inward sufficiently to be easily passed through a receiving hole in the tip of the spring leaf. The tip insert has a pin of sufficient length to partially or totally fill the shank bore to achieve the desired force for removal. This pin is inserted into the bore of the shank, using a hammer or other suitable means, after the shank has been passed through the receiving hole in the spring leaf. The pin retains the shank protuberances in a position to extend radially outward to overlap the exit edge of the receiving hole in the spring leaf and produces high resistance to their inward deflection and compression to pass back in reverse through the hole in the spring leaf and disengage from the leaf spring. To provide additional ease of installation, the pin is integrally molded with the pad portion and the shank portion of the tip insert. To install the pin, the pin is simply pressed into the underlying bore of the tip insert shank portion using a mallet or other suitable means after the shank portion has been easily inserted through the receiving hole in the leaf spring.
The pin is typically designed to have either or both an interference fit and a mating mechanical locking feature to engage within the shank bore of the tip insert when the pin is inserted into said shank bore to assure retention of the pin in vehicle service and its effectiveness in preventing the shank and protuberances from inward deflection and disengagement of the tip insert from the spring leaf.
It is a desire of the present invention to provide a leaf spring tip insert that has a low force requirement for installation and a high force requirement for removal or disengagement of the insert from the leaf spring.